1. Field of the Invention:
The present invention relates to the field of pseudo-random number generation and digital video systems. More specifically, the present invention relates to the generation of replicable pseudo-random numbers in a digital video system.
2. Background
A pseudo-random number generator generates a sequence of random numbers starting from a first random number by means of an initial value of zero and a predetermined algorithm. The predetermined algorithm is first applied to the initial value of zero to generate the first random number. The predetermined algorithm is then applied again to the first random number to generate the second random number. Each successive random number is generated in this manner, applying the predetermined algorithm to the previously generated random number. Although the pseudo-random numbers are predetermined by the initial value and the chosen algorithm, they provide a good approximation for random numbers that are mutually independent and uniformly distributed in a given interval.
Various digital apparatus for generating pseudo-random sequence are known. Included among these apparatus are those that use what's known as the generalized feedback shift register (GFSR) process. Typically, in these GFSR process based pseudo-random number generators, an n-bit pseudo-random number is obtained by serially shifting out n bits from a shift register or a shift register chain. Inputs are serially loaded in the shift register or shift register chain.
The focus of successive generations of pseudo-random number generators has been primarily on improving the length of the pseudo-random number sequence before the generated pseudo-random numbers would start to repeat themselves. However, for many digital video applications, including controllable dynamic companding the sequence length requirement is not very long. An equally important requirement is the requirement for the pseudo-random number generation to be controllable and repeatable. In other words, it is important for the pseudo-random number sequence to be repeatable within a specified area of the video image, such as a field, a line or a frame. As will be disclosed, the method and apparatus of the present invention for generating pseudo-random numbers based on a video control counter achieves the above described desirable results.